1) Field of the Invention
The present invention relates to a scroll type compressor which can be used, for example, in an air-conditioning system of a vehicle such as an automobile, and more particularly, to a scroll type compressor provided with an improved bearing arrangement for a drive shaft thereof.
2) Description of the Related Art
A scroll type compressor is well known as a compressor for an air conditioning system of an automobile, and comprises immovable and movable scroll members housed in a housing and having spiral guide walls engaged with each other in such a manner that spaces are formed therebetween. The movable scroll member is revolved around a center axis of the immovable scroll member in such a manner that the engagement is maintained between the spiral guide walls of the immovable and movable scroll member, and that the spaces therebetween are displaced toward centers of the spiral guide walls. During the revolution of the movable scroll member around the center axis of the immovable scroll member, a space appears successively at the outsidemost portions of the spiral guide walls thereof, and opens to take in a refrigerant, including a lubricating oil mist, fed from an evaporator of the air conditioning system, and then the space concerned is fully closed by the spiral guide walls due to the revolution of the movable scroll member. Thereafter, as the space concerned is displaced toward the centers of the spiral guide walls, a volume thereof becomes gradually smaller, whereby the refrigerant confined therein is compressed, and when the space concerned reaches the centers of the spiral guide walls, the compressed refrigerant is discharged into a discharge chamber formed in the housing of the compressor. Thereafter, the space concerned disappears at the centers of the spiral guide walls, and thus a compression of the refrigerant is successively carried out.
To cause the revolution of the movable scroll member around the central axis of the immovable scroll member, the compressor further comprises a drive shaft operatively connected to and rotated by a prime motor of the vehicle, and an eccentric mechanism provided between the drive shaft and the movable scroll member for converting the rotation of the drive shaft into the revolution of the movable scroll member. During the revolution of the movable scroll member, i.e., the compression of the refrigerant, a large force resulting from the compressed refrigerant is exerted upon the drive shaft in a cantilever manner, and accordingly, the drive shaft must be rotatably supported by at least two radial bearings spaced apart from each other along a longitudinal axis thereof. In this case, the smaller the distance between the two radial bearings, the larger the load to which the radial bearing adjacent to the eccentric mechanism is subjected, due to the force exerted upon the drive shaft, and thus the service life of the radial bearing adjacent to the eccentric mechanism is greatly shortened. By increasing the distance between the two radial bearings, the load to which the radial bearing adjacent to the eccentric mechanism is subjected can be reduced, whereby the service life of the bearing can be prolonged, but the size of the compressor is increased due to the larger distance between the two radial bearings.
Japanese Unexamined Patent publication No. 60-101295 discloses an arrangement wherein a seal assembly for the drive shaft is disposed between the two radial bearings, so that the distance therebetween can be increased without increasing the size of the compressor, but this arrangement is not completely satisfactory because the bearing disposed at the outside of the seal assembly cannot be lubricated with the oil mist included in the refrigerant; namely, the outer bearing must be lubricated with grease. In this case, a suitable amount of grease must be periodically supplemented to the outer bearing, and dust may be included in the grease applied to the outer bearing, during this supplementing of the grease.
Japanese Unexamined Patent publication No. 60-233389 discloses an arrangement wherein the two radial bearings are disposed at the inside of the seal assembly for the drive shaft. In this arrangement, both bearings can be lubricated with the oil mist included in the refrigerant, but the distance between the two bearings is reduced, and accordingly, the load to which the bearing adjacent to the eccentric mechanism is subjected is increased, resulting in a shortening of the service life thereof. Although a stronger and larger bearing can be used as the bearing adjacent to the eccentric mechanism, this is expensive and the larger size thereof results in an increase of the size of the compressor.